Thermal doping of materials

ABSTRACT

A method is disclosed for doping a semiconductor material comprising the steps of providing a semiconductor material having a first and a second surface. A dopant precursor is applied on the first surface of the semiconductor material. A thermal energy beam is directed onto the second surface of the semiconductor material to pass through the semiconductor material and impinge upon the dopant precursor to dope the semiconductor material thereby.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part of U.S. patent application Ser. No.14/563,880 filed Dec. 8, 2014. U.S. patent application Ser. No.14/563,880 filed Dec. 8, 2014 claims benefit of U.S. Patent Provisionalapplication No. 61/948,006 filed Mar. 4, 2014 and claims benefit of U.S.Patent Provisional application No. 61/936,078 filed Feb. 5, 2014 andclaims benefit of U.S. Patent Provisional application No. 61/914,364filed Dec. 10, 2013. All subject matter set forth in U.S. patentapplication Ser. No. 14/563,880 and provisional application Nos.61/948,006 and 61/936,078 and 61/914,364 is hereby incorporated byreference into the present application as if fully set forth herein.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to semiconductors and more particularly to anapparatus and a method for providing a high concentration of dopant intoa semiconductor material.

Description of the Related Art

Compact high voltage fast photoconductive semiconductor switches (PCSS)require wide-bandgap compound semiconductors, particularly siliconcarbide, with a high concentration, deep doping of N-type dopant thatcontributes electrons to the conduction band. Silicon carbide underevaluation for these applications requires maximizing n-type dopantconcentrations and depths not achieved by ion implantation.

The increase in dopant concentration and depth overcomes the majordisadvantage of silicon carbide high-power, high-temperaturephotoconducting devices, namely, high trigger energies for linera-modeoperation (Colt J., Hettler C., and Dickens J., “Design and Evaluationof a Compact Silicon Carbide Photoconductive Semiconductor Switch”,IEEE: Transactions on Electron Devices, Vol. 58, No. 2., February 2011,pp 508-511).

US Published application US20120082411A1 to Sullivan et al discloses ahigh voltage photo switch package module.

High pressure doping of wide bandgap (compound) semiconductor substratessuch as wafers can not be conducted by ion implantation since ionimplantation is a high vacuum process. For example, ion implantation ofnitrogen in silicon carbide has achieved dopant depths on the order ofonly 100 nm, and creates surface degradation/non-stoichiometry.

The prior art includes (Aoki T., Hatanaka Y., Look, D. C., “ZnO DiodeFabricated by Excimer-Laser Doping” (2002) Applied Physics Letters,76(22), 3257-3258) excimer laser doped oxygen and nitrogen into zincoxide at a maximum pressure of 4 atmospheres (58.8 psi). The doped layerwas estimated to be approximately 50 nm.

The present invention is an improvement to above prior art and arefurther developments of semiconductors and wide bandgap materials usingthermal energy beams or laser beams by the instant inventor Nathaniel R.Quick PhD. Discussion of semiconductors and wide bandgap materials andthe processing thereof using thermal energy beams or laser beams are setforth in the following U.S. Patents that are hereby incorporated byreference into the present application as if fully set forth herein:U.S. Pat. No. 5,145,741; U.S. Pat. No. 5,391,841; U.S. Pat. No.5,793,042; U.S. Pat. No. 6,732,562; U.S. Pat. No. 5,837,607; U.S. Pat.No. 6,271,576; U.S. Pat. No. 6,025,609; U.S. Pat. No. 6,054,375; U.S.Pat. No. 6,670,693; U.S. Pat. No. 6,939,748; U.S. Pat. No. 6,930,009;U.S. Pat. No. 7,013,695; U.S. Pat. No. 7,237,422; U.S. Pat. No.7,268,063; U.S. Pat. No. 7,419,887; U.S. Pat. No. 7,951,632; U.S. Pat.No. 7,811,914 and U.S. Pat. No. 7,897,492.

Therefore, it is an objective of this invention is to provide anapparatus and a method for providing a high concentration of dopant intoa material.

Another objective of this invention is to provide an apparatus and amethod for forming a material having a dopant solubility to maximumsolubility greater than (10²⁰ atoms/cc nitrogen in SiC).

Another objective of this invention is to provide a material having adopant solubility to maximum solubility greater than 1020 atoms/ccnitrogen in SiC.

Another objective of this invention is to provide a catalyst having highenergy site.

Another objective of this invention is to provide an apparatus and amethod for making a material having a high concentration of dopantthrough laser processing.

Another objective of this invention is to provide an apparatus and amethod for making a material having a high concentration of dopantthrough a plasma arc lamp processing.

The foregoing has outlined some of the more pertinent objects of thepresent invention. These objects should be construed as being merelyillustrative of some of the more prominent features and applications ofthe invention. Many other beneficial results can be obtained bymodifying the invention within the scope of the invention. Accordinglyother objects in a full understanding of the invention may be had byreferring to the summary of the invention, the detailed descriptiondescribing the preferred embodiment in addition to the scope of theinvention defined by the claims taken in conjunction with theaccompanying drawings.

SUMMARY OF THE INVENTION

The present invention is defined by the appended claims with specificembodiments being shown in the attached drawings. For the purpose ofsummarizing the invention, the invention relates to a method for dopinga semiconductor material comprising the steps of providing asemiconductor material having a first and a second surface. A dopantprecursor is applied a on the first surface of the semiconductormaterial. A thermal energy beam is directed onto the second surface ofthe semiconductor material to pass through the semiconductor materialand impinge upon the dopant precursor to dope the semiconductor materialthereby.

In a more specific example of the invention, the step of thesemiconductor material is selected from the group consisting of galliumnitride, silicon carbide and zinc oxide. The semiconductor material is asemiconductor material transparent to the frequency of the thermalenergy beam.

In still another embodiment of the invention, the step of applying adopant precursor includes applying a gas dopant precursor to the firstsurface of the semiconductor material. In the alternative, the step ofapplying a dopant precursor includes applying a thin film dopantprecursor or a powder dopant precursor to the first surface of thesemiconductor material.

Preferably, the step of irradiating the substrate with a thermal energybeam includes directing a 532 nm wavelength thermal energy beam onto thesecond surface of the semiconductor material to pass through thesemiconductor material and impinge upon the dopant precursor to dope thesemiconductor material thereby. The thermal energy beam may be a laserbeam or a high density plasma arc lamp.

The foregoing has outlined rather broadly the more pertinent andimportant features of the present invention in order that the detaileddescription that follows may be better understood so that the presentcontribution to the art can be more fully appreciated. Additionalfeatures of the invention will be described hereinafter which form thesubject of the claims of the invention. It should be appreciated bythose skilled in the art that the conception and the specificembodiments disclosed may be readily utilized as a basis for modifyingor designing other structures for carrying out the same purposes of thepresent invention. It should also be realized by those skilled in theart that such equivalent constructions do not depart from the spirit andscope of the invention as set forth in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

For a fuller understanding of the nature and objects of the invention,reference should be made to the following detailed description taken inconnection with the accompanying drawings in which:

FIG. 1 is a top view of a first apparatus for doping a semiconductorsubstrate in accordance with the present invention;

FIG. 2 is a side sectional view along line 2-2 in FIG. 1;

FIG. 3 is an isometric view of a photo conductive semiconductor switchfabricated in accordance with the process of the present invention;

FIG. 4 is a side sectional of a second apparatus for doping asemiconductor substrate in accordance with the present invention;

FIG. 5 is an energy dispersive X-ray spectrum of X-ray photon countverses the energy level of the energy in X-ray photon count for an SiCsubstrate ureated by the present invention.

FIG. 6 is an energy dispersive X-ray spectrum of X-ray photon countverses the energy level of the energy in X-ray photon count for a SiCsubstrate doped in accordance with the method of the present invention;

FIG. 7 is a scanning electron microscope micrograph (SCM) of a SiCsubstrate doped in accordance with the method of the present invention;

FIG. 8 is an angled scanning electron microscope micrograph (SCM) viewof a SiC substrate doped in accordance with the method of the presentinvention;

FIG. 9 is a side sectional view of a third apparatus for doping atransparent substrate in accordance with the present invention;

FIG. 10 is a magnified view of a semiconductor material with a precursordoping material being irradiated through the semiconductor material; and

FIG. 11 is a magnified view of a semiconductor material with a precursordoping material and located on a substrate being irradiated through thesubstrate and the semiconductor material.

Similar reference characters refer to similar parts throughout theseveral Figures of the drawings.

DETAILED DISCUSSION

FIG. 1 is a side view of an apparatus 5 for forming a dopedsemiconductor substrate 10 in accordance with the present invention. Thesubstrate 10 defines a first and a second side 11 and 12 and aperipheral edge 13. Preferably, the substrate 10 is a wide bandgapsemiconductor substrate. In this example, the substrate 10 is a siliconcarbide (SiC) semiconductor substrate.

The substrate 10 is shown located in an air-tight chamber 20. Theair-tight chamber 20 comprises a side wall 21 interconnected by a bottomwall 25 defining an interior space 26. A port 31 is located in the sidewall 21 of the chamber 20 for injecting and removing gases into and outof the chamber 20.

A closure 40 is adapted to mate with the chamber 20 to form an airtightseal. The closure 40 includes a light transmitting window 42. Theclosure 40 includes plural apertures 44 for receiving the plural studs38 extending from the chamber 20. Fastening nuts 46 secure the closure42 the chamber 20.

A seal 50 is disposed between the chamber 20 and the closure 40.Preferably, the seal 50 is formed of a resilient material such asfluoropolymer elastomer or the like. The seal 50 enables the substrate10 to be processing in a selected atmosphere.

A laser 60 is directed into a scanner 62 for creating a focused laserbeam 64 to pass through the light transmitting window 42 and to impingeupon the first side 11 of the substrate 10. The scanner 62 enables thefocused laser beam 64 to be positioned at various locations on the firstside of the substrate 10. Preferably, the laser 60 and the scanner 62are controlled by a computer 66.

A doping gas 70 is applied to the first side 11 substrate 10. In thisexample, a Nitrogen gas 72 is applied to the first side 11 of thesubstrate 10 under an ultra high pressure of 500 pound per square inchor greater.

The laser beam 64 is focused onto the first side 11 of the substrate 10to inject atoms from the doping gas into the substrate 10. The laserbeam 64 is focused onto the first side 11 of the substrate 10 toprocesses selected areas of the substrate 10 within the chamber 20. Inthe alternative, the laser beam 64 injects atoms from the doping gasinto the entirety of the substrate 10. The laser beam 64 is focused ontothe top surface region or through the substrate to the top surfaceregion within the chamber 20.

FIG. 3 is a top view of photo conductive semiconductor switch 80incorporating a doped semiconductor 10A in accordance with the presentinvention. The photo conductive semiconductor switch 80 comprises thephoto-conductive substrate 10A bonded with two waveguides 81 and 82. Anexample of a photo conductive semiconductor switch is set forth in USpatent publication US20120082411A1 to Sullivan which is incorporated byreference as if fully set forth herein. It should be understood that thephoto conductive semiconductor switch 80 is merely one example ofvarious devices semiconductor devices that may incorporate a dopedsemiconductor 10 in accordance with the present invention.

FIG. 4 is a side view of a second apparatus 6 for forming for forming adoped semiconductor 10 in accordance with the present invention. Thechamber 20 is identical to the chamber shown in FIGS. 1 and 2. Theapparatus 6 comprises a high density plasma arc lamp 90 for irradiatingthe substrate 10 within the chamber 20. The plasma lamp 90 is powered bya power supply 92 to provide a plasma beam 94. The plasma lamp 90 iscontrolled by a computer 96. The computer 96 controls the intensity,pulse duration and the pulse frequency of the plasma lamp 90. Theelectromagnetic radiation emanating from the plasma lamp 90 istransmitted through the light transmitting top window 42 of the closure40 to irradiate the substrate 10 in accordance with a computer programstored in the computer.

A suitable plasma lamp 90 is described in U.S. Pat. No. 4,937,490 andU.S. Pat. No. 7,220,936 that are incorporated by reference into thepresent specification as if fully set forth herein. The plasma lamp 90can supply large power densities, (up to 20,000 Watts/square centimeter)over large areas (4 square meters) in short time frames (0.5microseconds to 10.0 seconds).

The plasma lamp 90 is capable of quickly delivering large amounts ofheat over large surface areas with little or no deleterious influenceupon subsurface compositions. The computer 96 controls the pulse energyfrom the plasma lamp 90 in both duration and/or periodicity to allowprecise control various process parameters. In the process of thepresent invention, the plasma lamp 90 with a dominate wavelengthemission near 532 nm, is used for processing large areas or the entiretyof the substrate 10.

The electromagnetic radiation emanating from the plasma lamp 90 istransmitted through the light transmitting top window 42 of the chamber20 to irradiate the substrate 10 in accordance with a computer programstored in the computer. The interior space 26 of the chamber 20 isfilled with a high pressure doping gas 90. The high pressure doping gas90 is applied to the first side 11 substrate 10. In this example, aNitrogen gas 70 is applied to the first side 11 of the substrate 10under an ultra high pressure of 500 pound per square inch or greater.

The apparatus 5 of FIGS. 1 and 2 is best suited for forming a dopedsemiconductor 10 in selected areas of the semiconductor substratewhereas the second apparatus 6 is best suited for forming a dopedsemiconductor 10 over the total surface area of the semiconductorsubstrate.

The high doping gas pressure (nitrogen) reduces and eliminatessublimation and/or degradation of the silicon carbide surface. The highdoping gas pressure (nitrogen) increases the solubility of nitrogen insilicon carbide. Sievert's Law states that solubility increase directlywith the square root of gas pressure. (Sievert's Law applies to diatomicgases such as nitrogen which dissociate to atoms before diffusing into ametal or semiconductor). This is important for highly defect freesilicon carbide which has limited defects (dislocations, voids,micropipes) to assist in gas entry into the substrate.

The maximum solubility of nitrogen in silicon carbide has been reportedto be 6×10²⁰ atoms/cc (Ref. G. L. Harris, Published by INSPEC, theInstitution of Electrical Engineers, London, United Kingdom, 1995, pg153-155.)

EXAMPLE I Laser Nitrogen Doping of a Semi-Insulating 4H-SiC ContainingApproximately 1×10¹⁷ to 2×10¹⁷ Atoms/cc Vanadium (10 mm×5.6 mm×1000Micron Substrate) Process Parameters

-   -   Laser Source: 532 nm wavelength    -   Power: 55 watts    -   Frequency: 10 KHz    -   Duration: 8 microsec    -   Beam diameter: 100 micron    -   Scan rate: 2 mm/s    -   Scan number: 100    -   Gas: UHP Nitrogen    -   Gas pressure: 520 psi

Characterization and Analysis Field Emission SEM (FESEM)/EnergyDispersive X-Ray (EDX)

The doped nitrogen concentration was measure directly by refining aField Emission SEM (scanning electron microscope)/EDX(energy dispersivex-ray) technique to evaluate the semi-insulating (vanadium-doped)samples. The depth of the electron beam interaction volume was about 1-2micron. The samples require no electrically conductive coating.

-   -   Microscope: FESEM/EDX (Zeiss Ultra 55, Gemini)    -   Acceleration Voltage: 5.0 KV    -   Beam interaction depth: 1-2 micron

Chemical Analysis

FIG. 5 is an energy dispersive X-ray spectrum of X-ray photon countverses the energy level of the energy in X-ray photon count for a SiCsubstrate doped in accordance with the method of the prior art. Thebaseline detection for nitrogen in an untreated surface area of thesemi-insulating SiC is 1.71 atom %. This number is taken as the baselinefor nitrogen detection.

FIG. 6 is an energy dispersive X-ray spectrum of X-ray photon countverses the energy level of the energy in X-ray photon count for a SiCsubstrate doped in accordance with the method of the present invention.The a SiC substrate doped in accordance with the method of the presentinvention exhibits an increased nitrogen peak at approximately 0.0.4keV.

Exposure to 100 scans shows a nitrogen concentration of 4.01 atom %, aneighboring area showing no topological change shows a nitrogenconcentration of 1.55 atom % comparable to the 1.71 atom % baseline.Therefore, the laser treated area shows a nitrogen concentration, c[N]˜1to 2 atom % given the baseline and error. This is equivalent to 4.8×10²⁰to 9.6×10²⁰ atoms/cc. Nitrogen has been incorporated by laser dopinginto the semi SiC substrate.

Structural

FIG. 7 is an angled scanning electron microscope (SCM) micrograph viewof a SiC substrate doped in accordance with the method of the presentinvention. The micrograph was taken at a tilt angle of 59 degrees. Themicrograph shows an array of cone like structures across the surfacewhere a surface change is observed. The base of each cone is about 10-20micron with a height of 10-20 microns. The surface structure increasesthe effective surface area of the SiC substrate. The increased surfacearea is beneficial in photon trapping and hence energy absorption. Thedoped surface area, the majority of the micrograph, has a greatereffective surface area relative to the non-doped surface areaillustrated by the flat area in the upper right hand corner of themicrograph.

A more sparse cone array structure was observed; some. Note that somefeatures of the structure was formed for all scan numbers; it contrastand continuity of these features decreased with decreasing scan number.

The chemical measurement sensitivity of the FESEM/EDX shows no change incarbon concentration of this surface transition. The surface transitionfeatures are associated with morphological changes including crystalstructure.

This structure observed on a companion substrate exhibiting the samemorphological change showed a resistance of approximately 48 ohmsmeasured by 2 point probe. The as received substrate showed nomeasurable conductivity on an HP ohmmeter greater than the maximum Mohmscale (e.g., >100 Mohms) on an HP ohmmeter. The sister substrate wasused for electrical property measurement to prevent metal transfer fromthe probe tips and hence contamination for EDX examination.

EXAMPLE II Laser Nitrogen Doping of n-Type 4H-SiC Containing 10¹⁵ to10¹⁶ Atoms/cc Nitrogen (10 mm×10 mm×300 Micron Substrate)

For comparison an n-type doped 4H-SiC sample was laser doped at scansusing process parameters identical to those for the semi-insulatingsubstrate.

Chemical Analysis

As received n-type SiC, provided by Dow Corning, is reported to have anitrogen concentration of 10¹⁵ to 10¹⁶ atoms/cc. These levels where notdetectable by our FESEM/EDX procedure.

Exposure to 100 scans shows a nitrogen concentration of 3.01 atom %;while a neighboring area showing no topological change shows a nitrogenconcentration of 1.55 atom % comparable to the baseline 1.28 atom %.Therefore, the laser treated area shows a nitrogen concentration,c[N]˜0.5-1 atom % given the measurement error. Additional nitrogen hasbeen incorporated by laser doping into the N-type SiC substrate. Lowerscan numbers showed no detectable nitrogen incorporation.

Structural

FIG. 8 shows a cross section through the n-type SiC laser nitrogen doped100 scans. A more sparse cone array structure was observed than forexample 1: some cones exhibited a droplet formation at the top. Thecones have a height 10-30 micron: a band below the cones has a thicknessof about 1 micron. This region apparently has mechanical propertiesdifferent from the remainder of the bulk and is considered the maximumdepth of the laser-materials interaction. Therefore the thickness(average cone height plus region above the bulk) of the laser treatedarea is approximated at 20 microns.

This structure observed on a companion substrate exhibiting the samemorphological change showed a resistance of approximately 10 ohmsmeasured by 2 point probe. The as received substrate showed a resistanceof about 20 Mohm on an HP ohmmeter.

EXAMPLE III High Pressure Laser Doping of Gallium Nitride

Contact resistance and access resistance in deeply scaled PET devicesgreatly impact device performance at high frequency. This is ofparticular importance for GaN-based devices, which can achieve highpower at high frequencies (>100 GHz). Several processes have beendeveloped to address these resistance issues, but these processes allhave drawbacks. For example, ion implantation can be used to increasethe concentration of electrically active impurities in the source anddrain regions of the device, but this process requires high temperaturesfor electrical activation, along with capping layers to prevent GaNdecomposition. Additionally, implantation creates lattice damage that isdifficult to remove via annealing and acts to compensate the dopants.

To improve GaN device performance for high-frequency RF applications,the high pressure (greater than 500 psi gas/vapor precursor) laserdoping process is an improvement used to introduce electrically activen-type impurities into the source and drain regions of a GaN device toreduce contact resistance and decrease access resistance from the metalcontact to the two dimensional electron gas (2DEG) in the device.Silicon (Si) is the impurity chosen for n-type doping using a silaneprecursor. The preferred laser source is 532 nm wavelength.

To improve p-type doping, high pressure laser doping is used to injectmagnesium (Mg) atoms into the GaN substrate using a Bis-magnesiumdihydrate vapor precursor. This is an improvement over our low pressuredoping process where the vapor pressure does not exceed 15 psi.Preferred irradiation is with a 532 nm wavelength laser.

The high pressure laser doping process is a combination of a thermallydriven process resulting from the interaction of the semiconductor witha high-power, short-duration laser pulse and a pressure driven processto increase dopant concentration to maximum solubility levels at deepdepths while mitigating surface damage. The laser pulse results in anultra-fast thermal ramp (10¹⁰ K/s) and impurity incorporation throughdecomposition of chemisorbed gas-phase source species and thermaldiffusion of atoms into the crystalline lattice. Impurity incorporationrate, diffusivity, and activation are all functions of the laserwavelength, power, and pulse time and precursor pressure. A laser systemand processing chamber has been built for high pressure laser doping forrapid processing of substrates and simplification of the devicefabrication process.

EXAMPLE IV High Pressure Carbon Laser Doping of Gallium Nitride forPower Electronics

Silicon and carbon are amphoteric dopants that behave as a p-type dopantor n-type dopant depending on which lattice vacancy site they occupy.Select vacancy sites are created by effusion of gallium or nitrogenatoms. Precursors, including methane and acetylene are preferred carbonprecursors. Silane is a suitable precursor for silicon. Precursors aresubjected to high pressures, greater than 500 psi, for laser doping ofeither carbon or silicon into GaN.

EXAMPLE V High Pressure Doping of Carbon Doping of Silicon Wafers

The invention is expanded to carbon doping of silicon wafers (see U.S.Pat. Nos. 7,811,914 and 8,617,965) to create a surface region of siliconcarbide in silicon to accommodate GaN thin film deposition.

Representative semiconductor materials include wide bandgapsemiconductor such as SiC, AlN, ZnO, BN, DLC (diamond-like-carbon), GaN,silicon carbide regions in silicon and Tungsten Oxide. The processdisclosed in the invention applies to substantially all indirect bandgapsemiconductors including silicon, silicon carbide, boron nitride,aluminum nitride, diamond, DLC, and gallium phosphide. The process isapplicable to direct bandgap semiconductors (GaN, ZnO) and theirdopants. The dopants for solid state devices include Al, Se, Cr, V, N,Mg, Si, Ga, As, P and Sb from gaseous, metalorganic or solid (thin film,powder etc) precursors.

EXAMPLE V High Pressure Laser Surface Modification and Enhanced Activityof Catalytically Active Semiconductors

Reaction sites on catalysts are usually areas of specificcharacteristics such as ability to bind reactants. These areas are alsoregions that cause strains on chemical bonds due to physical andelectrostatic interactions with the reaction precursors. It is oftenfound that the sites most reactive are those of the highest surfaceenergy compared to the bulk of the material. Thus areas of defects suchas kinks and dislocations in the catalyst crystal structure prove to bevery reactive and sometimes reaction specific. In metals these areas canbe created by cold working exhibiting increased chemical reactivity inthe form of corrosion rate. Another way to create these higher energysites is to quench a high temperature structure and essentially freezethe high energy state. With semiconductor catalysts such as siliconcarbide high energy state freezing can be accomplished by lasertreatment. Surface temperatures in excess of 3000° F. can be achievedwith rapid cooling not attainable by other heat treatment methods. Forexample, treatment of semi-insulating 4H-SiC in high pressure nitrogen(greater than 500 psi) with a 532 nm wavelength beam and 700 MW/cm2irradiance resulted in the surfaces shown in FIGS. 7 and 8.

As can be seen in the image the surface consists of cones and valleys.This is a direct result of freezing of the molten SiC once the beam haspassed. With most reported methods of laser treatment of SiC if thesurface temperature is allowed to go above 2500° F. the Si vaporizes asis evident by the visible plume in the beam. With laser processing inhigh pressure the vapor pressure of the Si is suppressed by theincreased chamber pressure thus eliminating Si vaporization. Thisresults in sustaining original stoichiometry in the frozen high energysurface structure,

With current efforts for use of SiC in the areas ofelectrophotocatalytic reduction of CO2 and as a support for PEM fuelcell catalysts it is believed that the high energy structures of highpressure laser treated material could prove beneficial. The higherenergy of the treated material along with its increased surface areashould result in higher turnover of reactants not only for its directuse as a catalyst but also as a support due to its higher energyinteraction with active species.

It is believed that the use of high pressure doping as set forth abovewill increase the efficiency and the process and the end product setforth in my previous inventions including U.S. Pat. No. 5,145,741; U.S.Pat. No. 5,391,841; U.S. Pat. No. 5,793,042; U.S. Pat. No. 6,025,609;U.S. Pat. No. 6,732,562; U.S. Pat. No. 5,837,607; U.S. Pat. No.6,271,576; U.S. Pat. No. 6,025,609; U.S. Pat. No. 6,054,375; U.S. Pat.No. 6,670,693; U.S. Pat. No. 6,939,748; U.S. Pat. No. 6,930,009; U.S.Pat. No. 7,013,695; U.S. Pat. No. 7,237,422; U.S. Pat. No. 7,268,063;U.S. Pat. No. 7,419,887; U.S. Pat. No. 7,951,632; U.S. Pat. No.7,811,914: U.S. Pat. No. 7,897,492 and U.S. Pat. No. 8,080,836.

FIG. 9 is a side view of a third apparatus 5B for forming for doping asemiconductor material 10B in accordance with the present invention. Thesemiconductor material 10B defines a first or top surface 11B and asecond or bottom surface 12B. The third apparatus 5B is similar to theapparaii 5 and 5B shown in FIGS. 1-4 with similar parts being labeledwith similar reference numerals.

In this embodiment, a bottom tunnel 27B extends from the bottom wall 25Binto the chamber 20B. A second light transmitting window 42B isinterposed in the bottom tunnel 27B for enabling the thermal energy beam60B to irradiate the second or bottom surface 12B of the semiconductormaterial 10B. The thermal energy beam 60B may be laser or a plasma lamphas previously described. In addition, the third apparatus 5B enablesthe semiconductor material 10B to be simultaneously irradiated on boththe first or top surface 11B and the second or bottom surface 12B.

A doping gas 70B is applied to the first surface of the semiconductormaterial 10B. Preferably, the doping gas 70B is applied to the firstsurface 11B of the semiconductor material 10B under an ultra highpressure of 500 pound per square inch or greater.

The thermal energy bean 94B is focused onto the interface between thefirst surface 11B of the semiconductor material 10B and the doping gas70B to processes the semiconductor material 10B within the chamber 20B.The thermal energy beam 94B passes through the semiconductor material10B to processes the semiconductor material 10B with the doping gas 70Bat the first surface 11B of the semiconductor material 10B.

FIG. 10 is a magnified view of a semiconductor material 10C with aprecursor doping material 70C being irradiated through the semiconductormaterial 10C. In this example, the doping material 70C is applied to thefirst surface 11C of the semiconductor material 10C as a thin film 75C.Preferably, the thin film 75C is applied by a deposition process such asevaporation, sputtering and the like. The thermal energy beam 94C passesthrough the semiconductor material 10C to processes the thin film 75Cand the semiconductor material 10C at the first surface 11C of thesemiconductor material 10C.

FIG. 11 is a magnified view of a semiconductor material 10C with aprecursor doping material 70D being irradiated through the semiconductormaterial 10D. In this example, the semiconductor material 10C issupported upon a transparent substrate 15D. In one example, asemiconductor material 10D of a Gallium nitride wafer is disposed on asapphire (Al₂O₃) substrates 15D. In another example, a semiconductormaterial 10D of a Gallium nitride wafer is the is disposed on a glass(SiO₂) 15D.

The doping material 70D is applied to the first surface 11D of thesemiconductor material 10D as a powder 75D. Although the doping material70D as been shown as a powder 75D, it should be appreciated by thoseskilled in the art that doping material 70D may be various types ofprecursor doping materials 70D.

The thermal energy beam 94C passes through the transparent substrate 15Dand the semiconductor material 10D to processes the thin film 75D andthe semiconductor material 10D at the first surface 11D of thesemiconductor material 10D.

Tables A and B set forth examples of several semiconductor materials andthe appropriate doping material for forming both N-Type and P-TYPE dopedsemiconductors.

TABLE A N TYPE Semiconductor Gallium Nitride SiC ZnO Material (GaN)Doping Silicon Nitrogen Aluminum Material (Si) (N) (Al)

TABLE B P TYPE Semiconductor GaN SiC ZnO Material Doping MagnesiumAluminum Nitrogen Material (Mg) (Al) (N)

Contact resistance and access resistance in deeply scaled FET devicesgreatly impact device performance at high frequency. This is ofparticular importance for GaN-based devices, which can achieve highpower at high frequencies (>100 GHz). Several processes have beendeveloped to address these resistance issues, but these processes allhave drawbacks. For example, ion implantation can be used to increasethe concentration of electrically active impurities in the source anddrain regions of the device, but this process requires high temperaturesfor electrical activation, along with capping layers to prevent GaNdecomposition. Additionally, implantation creates lattice damage that isdifficult to remove via annealing and acts to compensate the dopants.

To improve GaN device performance for high-frequency RF applications,the high pressure (greater than 500 psi gas/vapor precursor) laserdoping process is an improvement used to introduce electrically activen-type impurities into the source and drain regions of a GaN device toreduce contact resistance and decrease access resistance from the metalcontact to the two dimensional electron gas (2DEG) in the device.Silicon (Si) is the impurity chosen for n-type doping using a silaneprecursor. The preferred laser source is 532 nm wavelength.

To improve p-type doping, high pressure laser doping is used to injectmagnesium (Mg) atoms into the GaN material using a Bis-magnesiumdihydrate vapor precursor. This is an improvement over our low pressuredoping process where the vapor pressure does not exceed 15 psi.Preferred irradiation is with a 532 nm wavelength laser.

The high pressure laser doping process is a combination of a thermallydriven process resulting from the interaction of the semiconductor witha high-power, short-duration laser pulse and a pressure driven processto increase dopant concentration to maximum solubility levels at deepdepths while mitigating surface damage. The laser pulse results in anultra-fast thermal ramp (10¹⁰ K/s) and impurity incorporation throughdecomposition of chemisorbed gas-phase source species and thermaldiffusion of atoms into the crystalline lattice. Impurity incorporationrate, diffusivity, and activation are all functions of the laserwavelength, power, and pulse time and precursor pressure. A laser systemand processing chamber has been built for high pressure laser doping forrapid processing of substrates and simplification of the devicefabrication process.

Gallium nitride wafers, gallium nitride on sapphire (Al₂O₃) substratesand gallium nitride on glass (SiO₂) substrates can be laser or plasmaarc lamp doped by applying a thin film of dopant precursor on theexposed (top) gallium nitride surface, by chemical vapor deposition,then directing laser or plasma arc lamp energy through the substrate andthrough the bottom surface of the gallium nitride region. The laser beamor plasma arc lamp energy is focused at the GaN-dopant precursorinterface or in the vicinity of the interface within the GaN, GaN, SiCand other widebandgap semiconductors generally have higher melting andsublimation points than the dopant precursor. For example, the meltingpoint of GaN is 2500° C. while the melting point of a silicon thin filmdopant precursor is 1414° C. Glass is of interest as an inexpensive GaNchip carrier since it is easily recycled by melting, reducing toxicpollution from disposed electronic hardware. A preferred laserwavelength is 532 nm for which sapphire, glass and gallium nitride allshow a degree of transmittance. As discussed in our patent U.S. Pat. No.9,059,079 we have refined plasma arc lamp emission to closely match thiswavelength. Silicon, used primarily as an n-type dopant of GaN,deposited on the exposed (top) gallium nitride surface is highlyabsorbent of this 532 nanometer wavelength, the silicon absorptioncoefficient is ˜1×E04/cm⁻¹ (G. E. Jellison and F. A. Modine, Appl PhysLett. 41, 2(1982) 180-182) compared to 1×E02 to 1×E03/cm⁻¹ for galliumnitride (O. Ambacher et al, Sol. State Common., 97(5) 1996, 365-370).The thickness of the silicon thin film determines the maximum dopantconcentration. A thickness of 300 nanometers over a 1 cm×1 cm areaprovides a reservoir 1.5×10E17 silicon atoms. Excess thin film dopantprecursor can be stripped from the surface.

This method can be used for other combinations of semiconductors andsubstrates that have a degree of transparency to a particular laserwavelength combined with a precursor dopant that absorbs thiswavelength. Laser irradiation through the substrate and through thesemiconductor bottom surface can be used in combination with gas, vaporand powder precursors in contact with the top surface of asemiconductor. For example, transparent vanadium doped semi-insulatingsilicon carbide wafer dies immersed in high pressure nitrogen for n-typedoping can be laser doped using this method. A Zinc oxide compoundsemiconductor is also transparent to 532 nm wavelength. Aluminum thinfilm can be used as a precursor for n-type doping and nitrogen gas forp-type doping. High pressures can be applied using ultra-high purityargon or nitrogen or other gases and vapors such as metal-organicsdepending on the desired dopant. This energy irradiation method furtherdecreases semiconductor surface damage and allows improved control ofthe p-n junction dimensions.

The present disclosure includes that contained in the appended claims aswell as that of the foregoing description. Although this invention hasbeen described in its preferred form with a certain degree ofparticularity, it is understood that the present disclosure of thepreferred form has been made only by way of example and that numerouschanges in the details of construction and the combination andarrangement of parts may be resorted to without departing from thespirit and scope of the invention.

What is claimed is:
 1. A method for doping a semiconductor materialcomprising the steps of: providing a semiconductor material having afirst and a second surface; applying a dopant precursor on the firstsurface of the semiconductor material at a pressure of at least 500 psi;and directing a thermal energy beam onto the second surface of thesemiconductor material to pass through the semiconductor material andimpinge upon the dopant precursor to dope the semiconductor materialthereby.
 2. A method for doping a compound semiconductor material as setforth in claim 1, wherein the semiconductor material is selected fromthe group consisting of gallium nitride, silicon carbide and zinc oxide.3. A method for doping a semiconductor material as set forth in claim 1,wherein the semiconductor material is a wide-bandgap semiconductor.
 4. Amethod for doping a compound semiconductor material as set forth inclaim 1, wherein the semiconductor material is a wide-bandgapsemiconductor; and the wide-bandgap semiconductor is selected from thegroup consisting of gallium nitride and silicon carbide.
 5. A method fordoping a semiconductor material as set forth in claim 1, wherein thesemiconductor material is a semiconductor material transparent to thefrequency of the thermal energy beam.
 6. A method for doping asemiconductor material as set forth in claim 1, wherein the step ofapplying a dopant precursor includes applying a gas dopant precursor orvapor dopant precursor to the first surface of the semiconductormaterial.
 7. A method doping a semiconductor material as set forth inclaim 1, wherein the step of applying a dopant precursor includesapplying an inert gas or inert vapor precursor to the first surface ofthe semiconductor material.
 8. A method for doping a semiconductormaterial as set forth in claim 1, wherein the step of applying a dopantprecursor includes applying a thin film dopant precursor to the firstsurface of the semiconductor material.
 9. A method for doping asemiconductor material as set forth in claim 1, wherein the step ofapplying a dopant precursor includes applying a powder dopant precursorto the first surface of the semiconductor material.
 10. A method fordoping a semiconductor material as set forth in claim 1, wherein thestep of directing the thermal energy beam onto the second surface of thesemiconductor material includes the step of directing a 532 nmwavelength thermal energy beam onto the second surface of thesemiconductor material to pass through the semiconductor material andimpinge upon the dopant precursor to dope the semiconductor materialthereby.
 11. A method for doping a semiconductor material as set forthin claim 1, wherein the step of directing the thermal energy beam ontothe second surface of the semiconductor material includes the step ofdirecting a laser beam onto the second surface of the semiconductormaterial to pass through the semiconductor material and impinge upon thedopant precursor to dope the semiconductor material thereby.
 12. Amethod for doping a semiconductor material as set forth in claim 1,wherein the step of directing the thermal energy beam onto the secondsurface of the semiconductor material includes the step of directing ahigh density plasma arc lamp onto the second surface of thesemiconductor material to pass through the semiconductor material andimpinge upon the dopant precursor to dope the semiconductor materialthereby.
 13. A method for doping a semiconductor material as set forthin claim 1, wherein the step of directing the thermal energy beam ontothe second surface of the semiconductor material includes focusing thethermal energy beam onto an interface of the dopant precursor and thefirst surface of the semiconductor material.
 14. A method for doping asemiconductor material comprising the steps of: providing asemiconductor material on a substrate; applying a dopant precursor onthe semiconductor material at a pressure of at least 500 psi; and;directing a thermal energy beam to pass through the substrate and thesemiconductor material to impinge upon the dopant precursor to dope thesemiconductor material thereby.
 15. A method for doping a semiconductormaterial as set forth in claim 13, wherein the step of providing asemiconductor material on a substrate includes providing a semiconductormaterial on a substrate selected from the group consisting of Al₂O₃ andSiO₂.
 16. A method for doping a semiconductor material as set forth inclaim 13, wherein the step of applying a dopant precursor includesapplying a gas dopant precursor or vapor dopant precursor on thesemiconductor material.
 17. A method for doping a semiconductor materialas set forth in claim 13, wherein the step of applying a dopantprecursor includes applying an inert gas or inert vapor precursor on thesemiconductor material.
 18. A method for doping a semiconductor materialcomprising the steps of: providing a semiconductor material having afirst and a second surface; applying a dopant precursor to the firstsurface of the semiconductor material; directing a first thermal energybeam onto the second surface of the semiconductor material to passthrough the semiconductor material and impinge upon the dopant precursorto dope the semiconductor material thereby; and directing a secondthermal energy beam onto the first surface of the semiconductor materialto impinge upon the dopant precursor to dope the semiconductor material.